Older Woman in Plain Dress and Day Cap, circa 1865

Ambrotypes (meaning, "imperishable pictures") were popular in the mid-1850s through the 1860s. Glass plates coated with photosensitive collodion were exposed in cameras while wet. The resulting image on glass, backed with black material, appeared as a photographic positive. Ambrotypes replaced daguerrotypes as an affordable and convenient alternative; however, improvements in photographic processes soon led to widespread adoption of the tintype.